Many popular rotors or irrigation sprinklers in the market today require the use of a screwdriver to set the watering arc. For example, some rotors have an arc adjust shaft accessible from a top of the rotor that, when turned, rotates an arc adjust gear keyed to an adjustable stop. The rotors typically have a fixed left stop and an adjustable right stop. Setting the watering arc can be a slow process of repeated screwdriver arc adjustments and arc setting checks before the desired arc setting is achieved. Typically, rotors of this type can be adjusted to spray within a watering arc of about 40° to 350°.
In the previously described designs, a bull gear is keyed to the nozzle base, allowing the nozzle base to be manually rotated, typically referred to as fast-forwarding, to quickly see the arc setting. This can be done both wet (under pressure) and dry. The stop at each edge is felt tactically by the click of the trip arm and the hard stop as the drive gear engages against the direction of fast-forwarding. Rather than fast-forwarding, an alternate method to determine the watering arc is to watch the unit rotate and trip on each side. This is not ideal because rotors do not typically rotate very quickly.
Fast-forwarding must be actuated towards the direction of drive engagement, both wet and dry. Attempting to back-drive the mechanism will likely break gears if a clutch is not present to take the abuse. When the nozzle base is fast-forwarded with the direction of the drive, the trip mechanism ratchets and prevents damage to the gears.